U.S. patent number 8,178,988 [Application Number 12/805,659] was granted by the patent office on 2012-05-15 for direct-drive wind turbine generator and bearing structure.
This patent grant is currently assigned to Mitsubishi Heavy Industries, Ltd.. Invention is credited to Tomohiro Numajiri.
United States Patent |
8,178,988 |
Numajiri |
May 15, 2012 |
Direct-drive wind turbine generator and bearing structure
Abstract
A direct-drive wind turbine generator is provided with: a main
shaft having one end connected to a rotor head of a wind turbine
rotor; a generator having a stator, a stator casing for supporting
the stator, and a rotor connected to the other end of the main
shaft; first and second bearings positioned between the rotor head
and the generator to rotatably support the main shaft; and a torque
support for supporting the stator casing. The second bearing is
positioned closer to the generator than the first bearing. The
first bearing is a bearing with an aligning capability, and the
second bearing is a bearing with no aligning capability.
Inventors: |
Numajiri; Tomohiro (Tokyo,
JP) |
Assignee: |
Mitsubishi Heavy Industries,
Ltd. (Tokyo, JP)
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Family
ID: |
44857011 |
Appl.
No.: |
12/805,659 |
Filed: |
August 12, 2010 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20110266806 A1 |
Nov 3, 2011 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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PCT/JP2010/057613 |
Apr 28, 2010 |
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Current U.S.
Class: |
290/44;
384/583 |
Current CPC
Class: |
F16C
23/06 (20130101); F03D 80/70 (20160501); F16C
25/083 (20130101); F16C 19/543 (20130101); Y02E
10/72 (20130101); F05B 2220/7066 (20130101); F16C
2360/31 (20130101); F16C 19/364 (20130101); F16C
19/386 (20130101) |
Current International
Class: |
F03D
9/00 (20060101); H02P 9/04 (20060101) |
Field of
Search: |
;290/44,55
;415/229,2.1,4.2,4.5 ;384/583,493,504,517,519,557,559,563 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2006-177268 |
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Jul 2006 |
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JP |
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2005-240978 |
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Apr 2010 |
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JP |
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Primary Examiner: Gonzalez; Julio
Attorney, Agent or Firm: Kanesaka; Manabu Berner; Kenneth M.
Hauptman; Benjamin J.
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATION
This is a continuation application of International Application No.
PCT/JP2010/057613, filed on Apr. 28, 2010.
Claims
What is claimed is:
1. A direct-drive wind turbine generator, comprising: a main shaft
having one end connected to a rotor head of a wind turbine rotor; a
generator having a stator, a stator casing for supporting said
stator, and a rotor connected to the other end of said main shaft;
first and second bearings positioned between said rotor head and
said generator to rotatably support said main shaft; and a torque
support for supporting said stator casing, wherein said second
bearing is positioned closer to said generator than said first
bearing and said second bearing includes first and second inner
rings, first and second outer rings, first rolling elements
provided between said first inner ring and said first outer ring,
second rolling elements provided between said second inner ring and
said second outer ring, and a biasing member, wherein a distance
between said second outer ring and said second inner ring is
variable, and wherein said biasing member biases said second outer
ring so that an inner face of said second outer ring comes close to
an outer face of said second inner ring, wherein said first bearing
is a bearing with an aligning capability, and wherein said second
bearing is a bearing with no aligning capability.
2. The direct-drive wind turbine generator according to claim 1,
wherein said second bearing is a double taper roller bearing.
3. The direct-drive wind turbine generator according to claim 1,
wherein said first bearing is a tapered roller bearing, a
cylindrical roller bearing, or a spherical bearing.
4. The direct-drive wind turbine generator according to claim 1,
wherein said second bearing further includes: a third inner ring; a
third outer ring; and third roller elements provided between said
third inner ring and said third outer ring.
5. The direct-drive wind turbine generator according to claim 1,
further comprising: a bearing housing which houses and supports
said second bearing, wherein said stator casing includes a concave
on an opposing face opposed to said bearing housing, and wherein an
end of the bearing housing is on the same plane with said opposing
surface or a portion of said bearing housing is positioned in said
concave.
6. The direct-drive wind turbine generator according to claim 1,
further comprising: a bearing housing which houses and supports
said second bearing, wherein said torque support includes a torque
support member connected to said bearing housing, and wherein said
torque support member extend in a radial direction of said main
shaft to connect said bearing housing and said stator casing.
7. A direct-drive wind turbine generator, comprising: a main shaft
having one end connected to a rotor head of a wind turbine rotor; a
generator having a stator, a stator casing for supporting said
stator, and a rotor connected to the other end of said main shaft;
first and second bearings positioned between said rotor head and
said generator to rotatably support said main shaft; a torque
support for supporting said stator casing; and a bearing housing
which houses and supports said second bearing, wherein said second
bearing is positioned closer to said generator than said first
bearing and said second bearing includes first and second inner
rings, first and second outer rings, first rolling elements
provided between said first inner ring and said first outer ring,
second rolling elements provided between said second inner ring and
said second outer ring, and a biasing member, wherein a distance
between said second outer ring and said second inner ring is
variable, wherein said biasing member biases said second outer ring
so that an inner face of said second outer ring comes close to an
outer face of said second inner ring, wherein said first bearing is
a bearing with an aligning capability, wherein said second bearing
is a bearing with no aligning capability, wherein said stator
casing includes a center plate opposed to said bearing housing, and
an outer circumferential plate connected to an outer edge portion
of said center plate, wherein said center plate is structured so
that a center portion thereof is depressed with respect to said
outer edge portion to provide a concave for said stator casing,
wherein said outer circumferential plate is structured so that a
protruding portion which protrudes from an outer edge of said
concave in a radially inward direction of said main shaft to
function as a torque support, wherein a part of said bearing
housing is housed in said concave and said protruding portion is
fitted into a groove provided for said bearing housing to connect
said stator casing and said bearing housing, and wherein said
second outer ring of said second bearing is movable with respect to
said bearing housing by using a line contact or point contact.
8. The direct-drive wind turbine generator according to claim 7,
wherein a spherical roller is inserted between said bearing housing
and said second outer ring.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a direct-drive wind turbine
generator and bearing structure suitable for the direct-drive wind
turbine generator, and in particular, relates to a structure for
supporting a main shaft and a generator in a direct-drive wind
turbine generator.
2. Description of the Related Art
One known form of wind turbine generators is the direct-drive wind
turbine generator. In a direct-drive wind turbine generator, a wind
turbine rotor and a generator are directly connected by a main
shaft, while the rotation of the wind turbine rotor is transmitted
to the electric generator by a speed-up gear with the number of
rotations increased in a geared wind turbine generator.
A direct-drive wind turbine generator requires special,
consideration in designing the structure for supporting the main
shaft and the generator, because the size of the generator is large
due to the use of a synchronous generator, and the generator and
the main shaft are directly connected. In general, the main shaft
is rotatably supported with two bearings, and a structure for
preventing rotations of the stator casing of the generator is
provided. Hereinafter, the structure for preventing rotations of
the stator casing of the generator is referred to as torque
support. Due to rotations of the main shaft, a torque is applied to
the stator casing of the generator in the circumferential direction
of the main shaft. It is a role of the torque support to support
the stator casing so that that the stator casing does not rotate
even when a torque is applied. One or two generator bearings may be
additionally provided between the main shaft and the stator casing
to support the stator casing thereby. A structure for rotatably
supporting the main shaft with two bearings and supporting the
stator casing with a torque support is disclosed in European Patent
Application No. EP1327073 B1 (Patent Document 1), European Patent
Application No. EP2014917 A1 (Patent Document 2) and corresponding
Japanese Patent Application Publication P2009-019625A (Patent
Document 3), and International Publication WO2007/111425 (Patent
Document 4), for example.
Here, bearings with the aligning capability (bearings that allows
flexing and tilting of the shaft) are used in general, as bearings
which support the main shaft of a wind turbine generator. This is
considered to be based on a technical idea that flexing of the main
shaft is generated in a direct-drive wind turbine generator and the
flexing needs to be absorbed. For example, EP1327073 B1 discloses
that bearings for supporting the main shaft allow flexing of the
main shaft (e.g. Claim 1). Additionally, International Publication
WO2007/111425 discloses that a toroidal roller bearing is employed
as a bearing near the rotor head and that a spherical roller
bearing is employed as a bearing near the generator, hence
compensating the misalignment and tilting of the main shaft.
According to a study by the inventor of the present invention,
however, the structure which supports a main shaft with two
bearings having the aligning capability and further supports the
stator casing with a torque support is not appropriate in order to
keep the gap between the stator and rotor constant. FIG. 8 shows
the reason. Considered in the following description is a structure
which supports a main shaft 103 with first and second bearings 101
and 102, and supports the torque working on a stator casing 106 of
a generator 105 in the circumferential direction of the main shaft
with a torque support 104, as shown in FIG. 3. Here, l.sub.1 is the
distance between the load point on the side of the rotor head and
the first bearing 101; l.sub.2 is the distance between the first
bearing 101 and the second bearing 102; and l.sub.3 is the distance
between the second bearing 102 and a point at which force works
from the torque support 104 to the stator casing 106. Additionally,
R.sub.1 and R.sub.2 are the support reaction forces applied by the
first bearing 101 and the second bearing 102, and R.sub.3 is the
support reaction force applied to the stator casing 106 by the
torque support 104.
When the two bearings (the first bearing 101 and the second bearing
102) for supporting the main shaft 103 both has an aligning
capability, angles of flexure .gamma..sub.1 and .gamma..sub.2 are
caused at the respective positions thereof. Due to the angle of
flexure .gamma..sub.2 and the distance I.sub.3, which is inevitably
present because of the layout of the wind turbine generator, the
support reaction force R.sub.3 is caused even when no torque is
worked on the torque support 104. Here, the magnitude of the
support reaction force R.sub.3 is the product of the spring
constant of the torque support 104 times the strain .delta..
The support reaction force R.sub.3 is not preferable, since an
unbalance of the gap between the stator and rotor of the generator
105 is caused. When a permanent magnet synchronous generator (PMSG)
is used as the generator 105, in particular, the problem of the
unbalance of the gap is significant. In detail, a permanent magnet
synchronous generator (PMSG), in which magnetic attractive forces
of field magnets and various electric forces work, requires surely
keeping the gap between the stator and rotor and reducing various
vibration mode displacements. Due to the support reaction force
R.sub.3, however, the stator casing 106 is displaced
correspondingly to the internal clearance of the generator bearing
and the stator casing 106 itself is slightly deformed. As a result
of the displacement corresponding to the internal clearance and the
deformation, an unbalance of the gap between the stator and rotor
is caused, and mode vibration due to bending is caused in addition
to the magnetic vibration caused by the rotation. Occurrence of a
bending mode vibration is not preferable in view of an increase in
the vibration of the wind turbine generator. Additionally,
occurrence of bending mode vibration increases fatigue loads and
causes a problem that structural members (e.g. the main shaft 103,
the torque support 104, and the stator casing 106) need to be
designed to have a high strength, resulting in the increase of the
weight.
SUMMARY OF THE INVENTION
Therefore, an object of the present invention is to provide a
technique for preventing the unbalance of the gap between the
stator and rotor of an electric generator in a direct-drive wind
turbine generator.
In an aspect of the present invention, a direct-drive wind turbine
generator is provided with: a main shaft heaving one end connected
to a rotor head of a wind turbine rotor; a generator including a
stator, a stator casing for supporting the stator, and a rotor
connected to the other end of the main shaft; first and second
bearings positioned between the rotor head and the generator to
rotatably support the main shaft; and a torque support for
supporting the stator casing. The first bearing is a bearing with
an aligning capability, and the second bearing, which is positioned
closer to the generator than the first bearing, is a bearing with
no aligning capability. A double taper roller bearing may be used
as the second bearing. Additionally, a tapered roller bearing, a
cylindrical roller bearing, and a spherical bearing may be used as
the first bearing, for example.
In one embodiment, the second bearing includes first and second
inner rings, first and second outer rings, first rolling elements
provided between the first inner ring and the first outer ring,
second rolling elements provided between the second inner ring and
the second outer ring, and a biasing member. The distance between
the second outer ring and the second inner ring is variable, and
the biasing member biases the second outer ring so that the inner
face of the second outer ring comes close to the outer face of the
second inner ring.
In the direct-drive wind turbine generator, it is preferable that
the second bearing is movable with respect to a bearing housing
which houses and supports the second bearing, and the bearing
housing and the second outer ring are coupled through a line
contact or a point contact. In this case, for example, a
cylindrical roller may be inserted between the bearing housing and
the second outer ring.
Additionally, it is also preferable that the second bearing further
includes a third inner ring, a third outer ring, and a third roller
element provided between the third inner ring and the third outer
ring.
It is preferable that the stator casing have a concave on an
opposing face positioned opposed to the bearing housing which
houses and supports the second bearing, and that an end of the
bearing housing is on the same plane with the opposing face or that
a part of the bearing housing is positioned inside the concave.
Additionally, it is also preferable when the torque support has a
torque support member connected to the bearing housing which houses
and supports the second bearing, that the torque support member
connects the bearing housing and the stator casing in the radial
direction of the main shaft.
The stator casing may have a center plate which is opposed to the
bearing housing, and an outer circumferential plate connected to an
outer edge portion of the center plate. In this case, the center
plate may be structured so that the center portion thereof is
depressed from the outer edge portion to provide the stator casing
with a concave, and that the outer circumferential plate is
structured to form a protruding portion which protrudes from the
outer edge of the concave portion in the radially inward direction
of the main shaft and functions as a torque support. In this case,
a part of the bearing housing is housed in the concave and the
protruding portion is fitted into a groove provided for the bearing
housing, hence connecting the stator casing and the bearing
stand.
In another aspect of the present invention, a bearing structure
includes first and second inner rings, first and second outer
rings, first rolling elements provided between the first inner ring
and the first outer ring, second rolling elements provided between
the second inner ring and the second outer ring, and a biasing
member. The distance between the second outer ring and the second
inner ring is variable, and the biasing member biases the second
outer ring so that the inner face of the second outer ring comes
close to the outer face of the second inner ring.
The present invention prevents an unbalance of the gap between the
stator and rotor of an electric generator in a direct-drive wind
turbine generator.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view showing the configuration of a wind
turbine generator in one embodiment of the present invention;
FIG. 2 is a sectional view showing the configuration of the wind,
turbine generator shown in FIG. 1;
FIG. 3 is a sectional view showing an example of the configuration
of a second bearing, which is positioned closer to the
generator;
FIG. 4A is a sectional view showing another example of the
configuration of the second bearing;
FIG. 4B is a sectional view showing still another example of the
configuration of the second bearing;
FIG. 4C is a sectional view showing still another example of the
configuration of the second bearing;
FIG. 4D is a sectional view showing the configuration of the second
bearing shown in FIG. 4C in detail;
FIG. 4E is a perspective view showing the configuration of this
second bearing shown in FIG. 4C in detail;
FIG. 5 is an enlarged sectional view showing the configuration of
the wind turbine generator shown in FIG. 1;
FIG. 6 is a perspective view showing the configuration of a wind
turbine generator in another embodiment of the present
invention;
FIG. 7A is a perspective view showing a configuration of a wind,
turbine generator in one embodiment of the present invention;
FIG. 7B is a sectional view showing the configuration of the wind
turbine generator shown in FIG. 7A; and
FIG. 8 describes a problem caused when two bearings both have the
aligning capability in a direct-drive wind turbine generator.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 is a perspective view schematically showing the
configuration of a wind turbine generator 1 in one embodiment of
the present invention. The wind turbine generator 1 of this
embodiment is structured as a direct-drive wind turbine generator,
and has the following configuration: The wind turbine generator 1
is provided with a tower 2 and a nacelle base 3. The nacelle base 3
is placed at the top of the tower 2 so as to allow the yaw
rotation. First and second bearing housings 5 and 6 are disposed on
the nacelle base 3, and a main shaft 4 is rotatably supported by
first and second bearings 8 and 9 (see FIG. 2) provided in the
first and second bearing housings 5 and 6, respectively. One end of
the main shaft 4 is connected to a rotor head (not shown) of a wind
turbine rotor, and the other end is connected to a generator 7. The
generator 7 is further connected to the second bearing housing 6 by
a torque support 20.
FIG. 2 is a sectional view of the wind turbine generator 1 of this
embodiment, seen from above. The generator 7 has a stator 11 and a
rotor 12. The stator 11 is supported by a stator casing 13. On the
other hand, the rotor 12 includes field magnets 14 opposed to the
stator 11, and a rotor plate 15 which supports the field magnets
14. The rotor plate 15 is connected to a sleeve 16 which is
connected to an end of the main shaft 4, and thereby the rotor 12
is connected to the main shaft 4. Although the sleeve 16 is
connected to an end of the main shaft 4 in the present embodiment,
the sleeve 16 and the main shaft 4 may be formed continuously or
integrated as one unit.
The sleeve 16 is provided with generator bearings 17 and 18, and
the stator casing 13 is supported by the generator bearings 17 and
18. Supporting the stator casing 13 with the generator bearings 17
and 18 provided on the main shaft 4 is effective for keeping the
gap between the stator 11 and the rotor 12 constant.
The torque support 20 connects the stator casing 13 and the second
bearing housing 6. In this embodiment, the torque support 20
includes a pin 21, a sleeve 22, and a rubber bush 23. The sleeve 22
is fixed to the stator casing 13, and the rubber bush 23 is
inserted into the sleeve 22. Additionally, the pin 21 is inserted
into the rubber bush 23, and the pin 21 is fixed to the second
bearing housing 6. The torque working on the stator casing 13 in
the circumferential direction of the main shaft 4 is supported with
the torque support 20 having the above-described configuration.
As mentioned above, the structure in which the main shaft is
supported by two bearings having the aligning capability and the
stator casing is supported by the torque support has a problem of
occurrence of the unbalance of the gap between the stator and rotor
of the generator. In order to address this problem, the wind
turbine generator 1 of this embodiment employs a bearing with no
aligning capability, namely, a bearing that does not allow tilting
of the main shaft 4, as the second bearing 9, which is a bearing
closer to the generator 7. On the other hand, a bearing with the
aligning capability is used for the first bearing 8. More
specifically, a tapered roller bearing, a cylindrical roller
bearing, or a spherical bearing is used as the first bearing 8, for
example. On the other hand, a double taper roller bearing is used
as the second bearing 9, for example.
FIG. 3 is a sectional view showing an example of the configuration
of the second bearing 9. The second bearing 9 is provided with an
inner ring 25, an outer ring 26, and toroidal rollers 27 and 28
provided therebetween. Although one toroidal roller 27 and one
toroidal roller 28 are shown in FIG. 3, it should be understood
that a plurality of toroidal rollers 27 are arranged in a row in
the circumferential direction of the main shaft 4, and that a
plurality of toroidal rollers 28 are arranged in a row in the
circumferential direction of the main shaft 4. The inner ring 25 is
attached to the main shaft 4, and the outer ring 26 is attached to
the second bearing housing 6. The inner ring 25 has a taper so that
a depression is formed at the center portion of the second bearing
9, and the outer ring 26 has a taper such that a convexity is
formed at the center portion of the second bearing 9. The toroidal
rollers 27 and 28 are arranged to have smaller radii toward the
center of the second bearing 9. With the above-described
configuration, the second bearing 9 rotatably holds the main shaft
4 without allowing tilting.
The use of a bearing with no aligning capability as the second
bearing 9 allows mechanically integrating a portion, of the main
shaft 4 closer to the generator 7 than the second bearing 9; the
sleeve 16; the rotor 12; and the stator casing 13 in operating the
wind turbine generator 1, avoiding occurrence of a relative
displacement among these members. In other words, the change in the
relative position relationship between the portion of the main
shaft 4 closer to the generator 7 than the second bearing 9; the
sleeve 16; the rotor 12; and the stator casing 13 is prevented, and
these members work as if these members are a single unit as a
whole. This is effective in terms of keeping the gap between the
stator 11 and the rotor 12 constant and preventing the unbalance of
the gap.
In this embodiment, where a bearing with no aligning capability is
used as the second bearing 9, it is preferable that a bearing
structure which reduces backlash of the second bearing 9, namely,
which reduces the space between rolling elements (balls or a
rollers) in the second bearing 9 and the inner ring 25 or the outer
ring 26, is employed in order to surely keep the gap. FIG. 4A shows
an example of the configurations of a second bearing 9A formed to
reduce the space and of a second bearing housing 6A for supporting
the second bearing 9A.
The second bearing housing 6A has a first annular member 36, an
intermediate member 37, a second annular member 38, a hold plate
39, and bolts 40. The intermediate member 37, the second annular
member 38, and the hold plate 39 are fixed to the first annular
member 36 by the bolts 40.
The second bearing 9A is provided with a first inner ring 31a, a
second inner ring 31b, a spacer 32, and a first outer ring 33a, a
second outer ring 33b, a spring 35, and toroidal rollers 34a and
34b. The first inner ring 31a, the second inner ring 31b, and the
spacer 32 are inserted onto the main shaft 4 and fixed to the main
shaft 4 by a nut 4a. The spacer 32 has a function to keep a desired
distance between the first inner ring 31a and the second inner ring
31b. The first inner ring 33a is held between the first annular
member 36 and the intermediate member 37. The second outer ring 33b
is held by being pressed against the inner face of the second
annular member 38. Here, the second outer ring 33b is slidable in
the axial direction of the main shaft 4.
The toroidal rollers 34a are inserted between the first inner ring
31a and the first outer ring 33a, and the toroidal rollers 34b are
inserted between the second inner ring 31b and the second outer
ring 33b. Here, although one toroidal roller 34a and one toroidal
roller 34b are shown in FIG. 4A, it should be understood that a
plurality of toroidal rollers 34a are arranged in a row in the
circumferential direction of the main shaft 4, and that a plurality
of toroidal rollers 34b are arranged in a row in the
circumferential direction of the main shaft 4.
The first inner ring 31a applies loads to the toroidal rollers 34a
in a radially outward direction toward the generator 7, which
direction is slanting with respect to the axial direction of the
main shaft 4. The second inner ring 31b applies loads to the
toroidal rollers 34b in a radially outward direction toward the
rotor head, which direction is slanting concerning the axial
direction of the main shaft 4. The first outer ring 33a applies
loads to the toroidal rollers 34a in a radially inward direction
toward the rotor head, which direction is slanting with respect to
the axial direction of the main shaft 4. The second outer ring 33b
applies loads to the toroidal rollers 34b in a radially inward
direction toward the generator 7, which direction is slanting with
respect to the axial direction of the main shaft 4. The
above-described configuration supports the axial load Fa and the
radial load Fr which work on the main shaft 4.
In addition, the spring 35 is inserted between the second outer
ring 33b and the intermediate member 37, and the second outer ring
33b is biased in the axial direction of the main shaft 4. Since the
outer face of the second inner ring 31b and the inner face of the
second outer ring 33b are tilted with respect to the axial
direction of the main shaft 4, the spring 35 hence biases the
second outer ring 33b so that the inner face of the second outer
ring 33b comes close to the outer face of the second inner ring
31b. The action of the spring 35 reduces the backlash of the second
bearing 9, namely, the space between the toroidal rollers 34b and
the second inner ring 31b, and the space between the toroidal
rollers 34b and the second outer ring 33b are reduced. The
above-described configuration allows mechanically integrating the
portion closer to the generator 7 than the second bearing 9 of the
main shaft 4; the sleeve 16; the rotor 12; and the stator casing
13, and effectively prevents occurrence of a relative displacement
among these members. This is effective in terms of preventing the
unbalance of the gap between the stator 11 and the rotor 12.
The bearing structure shown in FIG. 4A is also effective for
improving the uniformity of loads between the toroidal rollers 34a
and 34b, and for addressing the problem of the temperature
difference between the first and second inner rings 31a and 31b and
the first and second outer rings 33a and 33b. In the bearing
structure of FIG. 3, one row of toroidal rollers (e.g. the row of
the toroidal rollers 28) is burdened with a heavier load when a
load is applied in the axial direction of the main shaft 4. This is
undesirable, since the life of the second bearing 9 is shortened.
Additionally, the rotation of the main shaft 4 causes an increase
in the temperature of the second bearing 9, and the increase in
temperature is greater in the inner ring 25 than in the outer ring
26. When the temperature of the inner ring 25 is relatively higher
than the temperature of the outer ring 26, the thermal expansion of
the inner ring 25 is greater than that of the outer ring 26, and
consequently mechanical loads on the toroidal rollers 27 and 28 are
increased. This is undesirable, since the lives of the toroidal
rollers 27 and 28 are shortened.
As for the configuration in FIG. 4, on the other hand, the load Fa
equally works on the toroidal rollers 34a and 34b due to the action
of the spring 35, when the load Fa works on the second bearing 9 in
the axial direction. Therefore, the reduction of the lifetime due
to the heavy load applied to one row of toroidal rollers is
prevented. Additionally, in the case of the configuration in FIG.
4A, the thermal expansions of the first inner ring 31a and the
second inner ring 31b are absorbed by the spring 35 even when the
increase in the temperature of the first and second inner rings 31a
and 31b are greater than that of the first and second outer rings
33a and 33b. Therefore, the configuration in FIG. 4 can avoid the
problem of temperature difference between the first and second
inner rings 31a, and 31b, and the first and second outer rings 33a
and 33b.
To further reduce the displacement of the main shaft 4, three rows
of toroidal rollers may be provided as shown in FIG. 4B. In the
configuration of the second bearing 9B in FIG. 4B, a third inner
ring 31c and a third outer ring 33c are additionally provided, and
toroidal rollers 34c are provided therebetween. A spacer 32a is
provided between the first inner ring 31a and the third inner ring
31c while a spacer 32b is provided between the second inner ring
31b and the third inner ring 31c, hence keeping a desired space
between the first inner ring 31a and the third inner ring 31c and a
desired space between the second inner ring 31b and the third inner
ring 31c. Additionally, the first outer ring 33a and the third
outer ring 33c are held between the first annular member 36a and
the intermediate member 37. Here, a spacer 36b is inserted between
the first outer ring 33a and the third outer ring 33c, to keep a
desired space between the first outer ring 33a and the third outer
ring 33c.
It should be noted that balls may be used as rolling elements
instead of the toroidal roller 34a, 34b, and 34c, in the
configuration of FIG. 4B in which three rows of rolling elements
are provided. The use of balls as rolling elements is preferable in
terms of cost reduction.
In the configurations of FIGS. 4A and 4B, the second outer ring 33b
must be slidable in the axial direction on the inner face of the
second annular member 38. When the size of the second annular
member 38 is increased, manufacturing errors of the second annular
member 38 are also increased and this may make it difficult to
allow the second outer ring 33b to slide on the inner face of the
second annular member 38.
In order to allow the second outer ring 33b to move on the second
annular member 38, it is preferable that the contact between the
second outer ring 33b and the second annular member 38 is a line
contact or a point contact (not a face contact). This reduces the
friction between the second outer ring 33b and the second annular
member 38, allowing the second outer ring 33b to move on the second
annular member 38, more easily.
More specifically, cylindrical rollers 51 may be provided between
the second outer ring 33b and the second annular member 38 as shown
in FIG. 4C. Although only one cylindrical roller 51 is shown in
FIG. 4C, it should be understood in FIG. 4C that a plurality of
cylindrical rollers 51 are arranged in a row in the circumferential
direction of the main shaft 4. Each of the cylindrical rollers 51
is positioned so that the center axis thereof is parallel to the
axial direction of the main shaft 4. As shown in FIGS. 4D and 4E,
the cylindrical rollers 51 are retained at desired positions by a
retainer 52. As a result of the line contact between the
cylindrical rollers 51 and the second annular member 38 and the
line contact between the cylindrical rollers 51 and the second
outer ring 33b, the second outer ring 33b can move on the second
annular member 38, more easily. Although cylindrical rollers are
used in FIGS. 4C to 4E, balls may be used instead of cylindrical
rollers. Additionally, the structure in which cylindrical rollers
or balls are provided between the second outer ring 33b and the
second annular member 38 as shown in FIGS. 4C to 4E is also
applicable to the structure in which three rows of rolling elements
are provided as shown in FIG. 4B.
To further avoid the occurrence of the relative displacement
between the portion of the main shaft 4 closer to the generator 7
than the second bearing 9; the sleeve 16; the rotor 12; and the
stator casing 13, and further reduce the unbalance of the gap
between the stator 11 and the rotor 12, it is preferable to shorten
the distance in the axial direction of the main shaft 4 from the
position at which force works from the torque support 20 to the
stator casing 13, to the second bearing 9.
In order to achieve this, it is preferable that a concave portion
13a is provided for the stator casing 13a and that an end portion
6a of the second bearing housing 6 is positioned inside the concave
portion 13a of the stator casing 13, as shown in FIG. 5. In
addition, the end portion 6a of the second bearing housing 6 may be
on the same plane with an opposing surface 13b of the stator casing
13, which is opposed to the second bearing housing 6. In either
case, it is possible to shorten the distance in the axial direction
of the main shaft 4 between the position at which force works from
the torque support 20 to the stator casing 13, to the second
bearing 9.
FIG. 6 is a sectional view showing another configuration for
shortening the distance from the position at which force works from
the torque support to the stator casing 13, to the second bearing
9. In the structure of FIG. 6, a disk-shaped torque support member
24 is directly joined to the end portion of the second bearing
housing 6, and the stator casing 13 is connected to a peripheral
portion of the torque support member 24. An opening is provided at
the center of the torque support member 24, and the main shaft 4 is
inserted through the opening. It should be noted that, in the
structure of FIG. 6, the generator bearing 17 closer to the second
bearing 9 is not provided, since the distance between the second
bearing 9 and the stator casing 13 is short.
Such configuration enables positioning the position at which force
works from the torque support member 24 to the stator causing 13,
at the end of the second bearing housing 6. That is to say, the
torque support member 24 is formed to extend from the end of the
second bearing housing 6 in the radial direction of the main shaft
4 and to be connected with the stator casing 13, hence shortening
the distance from the position at which force works from the torque
support member 24 to the stator casing 13, to the second bearing 9.
This is effective in terms of further prevention of the occurrence
of the relative displacement between the portion of the main shaft
4 closer to the generator 7 than the second bearing 9; the sleeve
16; the rotor 12; and the stator casing 13.
It would be most ideal that the position at which force works from
the torque support 2C to the stator casing 13 is aligned with the
center of the second bearing 9. FIGS. 7A and 7B show a
configuration which allows aligning the position at which force
works from the torque support 20 to the stator casing 13 with the
center of the second bearing 9.
In the configurations of FIGS. 7A and 7B, a concave portion is
formed in the stator casing 13, and a part of the second bearing
housing 6C is housed in the concave portion. In detail, a front
plate of the stator casing 13 includes an outer circumferential
plate 41 and a center plate 42. The outer circumferential plate 41
is joined to the outer edge portion of the center plate 42. The
center plate 42 is depressed at the center portion thereof with
respect to the outer edge portion.
In addition, parts of the outer circumferential plate 41 protrude
in a radially inward direction from the joint with the center plate
42, and the stator casing 13 is supported by fitting the protruding
portions (protruding portions 41a) into grooves 44 of the second
bearing housing 6C. That is, the protruding portions 41a of the
outer circumferential plate 41 of the stator casing 13 function as
a torque support in this embodiment. In detail, the second bearing
housing 6C shown in FIG. 7A is provided with the grooves 44 and
openings 45 which cross and penetrate the grooves 44 in the axial
direction of the main shaft 4. On the other hand, openings 41b are
formed through the protruding portions 41a of the outer
circumferential plate 41. Pins 43 are inserted into the openings 45
of the second bearing housing 6C with the protruding portions 41a
of the outer circumferential plate 41 fitted into the grooves 44 of
the second bearing housing 6C. The pins 43 are inserted to
penetrate the openings 45 provided through the second bearing
housing 6C, and the openings 41b provided through the protruding
portions 41a of the outer circumferential plate 41. Consequently,
the stator casing 13 is fixed to the second bearing housing 6C.
Since the protruding portions 41a of the outer circumferential
plate 41 connect the center portion of the second bearing housing
6C and the stator casing 13 in a radial direction of the main shaft
4, the configuration shown in FIGS. 7A and 7B allows reducing the
distance from the position at which force works from the torque
support 2C to the stator casing 13, to the center of the second
bearing 9 in the axial direction of the main shaft 4, or ideally
allows the position at which force works from the torque support 20
to the stator casing 13 to be aligned with the center of the second
bearing 9. This is preferable in terms of further prevention of the
occurrence of the relative displacement between the portion of the
main shaft 4 closer to the generator 7 than the second bearing 9;
the sleeve 16; the rotor 12; and the stator casing 13, and further
reduction of the unbalance of the gap between the stator 11 and the
rotor 12.
* * * * *